In magnetic resonance imaging (MRI), the echo signals required for imaging apparatus construction are acquired by repeatedly executing an imaging sequence while varying a phase-encoding level, that is, the strength of a gradient magnetic field for phase encoding. Accordingly, an imaging time depends on the quantity of phase encoding and on a repetition time, and reduction of the imaging time is therefore desired.
A technique, termed “parallel imaging,” that uses multiple RF coils and image folding has started to be put into practical use as a technique for reducing the imaging time (hereinafter, this technique is called parallel imaging) [refer to Non-Patent Document 1].
To implement parallel imaging, it is necessary first to suppress mutual electromagnetic coupling between multiple sub-coils sufficiently. Electromagnetic coupling between the sub-coils causes noise interference to occur therebetween and deteriorates the S/N ratios of images. There is a need next to arrange the multiple sub-coils appropriately. Inappropriate arrangement of the sub-coils partly deteriorates the S/N ratios of the images. Among the criteria for evaluating the adequacy of the sub-coil arrangement is a criterion called the geometry factor (hereinafter, abbreviated to the G-factor). The G-factor is a value derived from the sensitivity distribution of each sub-coil in an imaging plane, and it is desired that the G-factor of an image section at which an object to be imaged is present should be as small as possible.
Parallel imaging is developed primarily on a horizontal magnetic field machine in high magnetic field strength, and various kinds of receiving coils adapted for horizontal magnetic field machines have been proposed. Arrangement forms of receiving coils adapted for vertical magnetic fields are proposed in Patent Documents 1 and 2. Vertical magnetic field MRI have the advantage that they allow the use of solenoid coils highly sensitive to depths of a subject, compared with horizontal magnetic field MRI. A solenoid coil, a two-turn solenoid coil (saddle coil) with sensitivity in a direction orthogonal to the former solenoid coil, and three sets of surface coils having sensitivity in x-, y-, and z-directions, respectively, are used in combination as coils highly sensitive to the depths of the subject, and these coils form the receiving coil of the vertical magnetic field MR imaging apparatus proposed in Patent Document 2. The use of these coils makes any phase-encoding direction selectable.    Non-Patent Document 1: J. B. Ra, C. Y. Rim: “Fast Imaging Using Subencoding Data Sets from Multiple Detectors,” Magnetic Resonance in Medicine, vol. 30, pp. 142-145 (1993)    Patent Document 1: JP-A-2002-153440    Patent Document 2: JP-A-2003-79595